A plurality of servers in a data center are connected to one another by a layer 2 (hereinafter referred to as “L2”) network. In the data center, a plurality of L2 networks are connected to one another via bridges (relay devices). Communication between servers connected to different L2 networks is carried out by using a bridge. With communication in the L2 network, the physical address (hereinafter referred to as a “media access control (MAC) address”) corresponding to a server to which a communication packet is destined (hereinafter referred to as the “destination server”) is specified in the communication packet, thereby allowing the communication packet to be delivered to the destination.
If a server from which a communication packet is sent (hereinafter referred to as the “source server”) has not yet acquired the MAC address corresponding to the destination server, an address resolution protocol (hereinafter abbreviated as an “ARP”) is followed before a communication packet is sent. As a result, the source server acquires the MAC address corresponding to the destination server.
With an ARP request, a packet, in which the destination Internet protocol (IP) address assigned to the destination server, the source MAC address corresponding to the source server, and the source IP address assigned to the source server are specified, is broadcast across an L2 network. A server that receives the broadcast ARP request sends MAC address of the server as an ARP reply in a unicast manner to the source server if the destination IP address specified in the packet matches the server's own IP address.
FIG. 1 illustrates an information processing system to which a related art technology has been applied. In FIG. 1, a rack 2, a rack 3 and a bridge 10 that are included in a data center 1 are illustrated. The rack 2 includes a network 4, as well as a server 6 and a server 7 connected to the network 4. The rack 3 includes a network 5, and a server 8 and a server 9 connected to the network 5. The network 4 and the network 5 are L2 networks, and the network 4 and the network 5 are connected to the bridge 10. For example, the server 6 communicates with the server 8 through the network 4, the bridge 10 and the network 5.
For example, assume that the source server is the server 6 and the destination server is the server 8. If the server 6 has not acquired the MAC address of the server 8, the server 6 broadcasts an ARP request across the network 4. The bridge 10 receives the ARP request and determines that the destination IP address included in the packet of the ARP request is the IP address of a server connected to the network 5, and then broadcasts the ARP request from the server 6 across the network 5. Since the IP address included in the packet of the received ARP request matches the IP address of the server 8, the server 8 sends the MAC address of server 8 as an ARP reply in a unicast manner to the server 6. By means of this ARP reply, the server 6 acquires the MAC address of the server 8. Thereafter, communication at a layer 3 (hereinafter referred to as “L3”) level is performed between the server 1 and the server 8.
By the way, it is known that the MAC address of a terminal belonging to an IP network connected to an asynchronous transfer mode (ATM) network is stored by an input/output (I/O) unit for the ATM network, and the I/O unit makes an ARP reply on behalf of the terminal. When the IP network is disconnected from the ATM network, the stored MAC address is deleted from the I/O unit.
[Patent Document] Japanese Laid-open Patent Publication No. 2004-64310